4 a.m. update: With much of the West Coast under a tsunami warning — meaning evacuation is recommended for coastal areas (more on that below) — Lori Dengler,professor of geology at Humboldt State University, just told CNN that the “series of surges” due to arrive in the next three or so hours have “the potential to look a little like what happened in 1964 along the West Coast, when there was quite a bit of damage of flooding in Oregon, Washington, Canada and … Crescent City.” The latter lost 11 people and suffered millions of dollars of damage from that tsunami.

Tonight, “coastal emergency managers are very busy working with first responders and public safety pepople to organize the process and evacuations,” Dengler said. “It’s not something that can be done lightly — people can be injured in the course of evacuating if it’s not done in a controlled way.

“The fortunate thing for us on the West Coast is we have a lot of time to get this done,” she continued, which is also helpful because “in much of this part of the West Coast, we’re dealing with very rural populations, unlike in Japan, where most people are within earshot of sirens. … We have very few ways of notifying people, television, radio, but this is the middle of the night.”

Asked what the tsunami could look like on the West Coast, given the horrific images from Japan, where the 8.9 earthquake late yesterday launched destructive waves, Dengler said, “It will look different in different places:

In some places it looks like a wall, in some places it looks like a sloping mountain of water, or a rapidly rising flood or a tide … The native people in our area, the Yurok people, described the earth tilting and the water flowing in.”

Yikes — I’m safely inland, but wanted to get the word out before I catch a little shut-eye. Aloha.

Original item:

As an aid to my California readers, some of whom are clicking on last year’s Alameda blog post about an tsunami advisory, let me state here that the coastal areas of Northern and Central California — from Point Concepion (Santa Barbara County) to the California-Washington-Oregon border — are now under a tsunami warning issued by the West Coast/Alaska Tsunami Warning Center, for waves expected to arrive as early as 7:17 a.m. (Cape Mendocino) and in San Francisco at 8:08 a.m. Friday (today.) You can find the list of expected arrival times along the coast here.

And a tsunami warning means “full evacuation suggested,” according to the center:

All coastal residents in the warning area who are near the beach or in low-lying regions should move immediately inland to higher ground and away from all harbors and inlets including those sheltered directly from the sea. Those feeling the earth shake, seeing unusual wave action, or the water level rising or receding may have only a few minutes before the tsunami arrival and should move immediately. Homes and small buildings are not designed to withstand tsunami impacts. Do not stay in these structures.

The coastal areas of California south of Point Concepcion to the Mexico border are under a tsunami advisory, meaning “strong currents likely; stay away from shore,” per the center, which explains:

Coastal regions historically prone to damage due to strong currents induced by tsunamis are at the greatest risk. The threat may continue for several hours after the arrival of the initial wave, but significant widespread inundation is not expected for areas under an advisory. Appropriate actions to be taken by local officials may include closing beaches, evacuating harbors and marinas, and the repositioning of ships to deep waters when there is time to safely do so.